A ribbon cable having a rolling loop can be used to provide an electrical connection between two parts. Under favorable conditions, the rolling loop contributes to a goal of maintaining precise control over relative movement between the two parts, which may include fixed and stationary parts within a tape drive. A force required to match the bias against movement caused by the rolling loop is generally very low, and also importantly, the force is substantially uniform throughout a required range of motion. These characteristics promote the precise control over movement required in most applications.
FIGS. 1–3 show three orthographic views of flexible ribbon cable 100 having a rolling loop 102. The rolling loop 102 typically forms a generally half-cylindrical or parabolic configuration about an axis 104. In FIG. 1, a top plan view shows the rolling loop 102 between first and second connectors 106, 108. FIG. 2 shows a side elevation view of the cable, wherein only one connector 108 is visible. FIG. 3 shows an orthographic view according to the 3—3 arrows of FIG. 1, showing an example of the rounded shape of the rolling loop 102. An arrow 302 indicates that, during operation in some applications, the connector 108 moves (e.g. up and down) relative to the connector 106 (which, for example, may be stationary).
In operation, the head unit—connected to the mobile connector 108—moves to position the head relative to tracks on the tape media. In the example tape drive unit 400 shown in FIG. 4, the head 402 may be moved very small distances to adjust its position with respect to an individual track on the tape and may be moved a somewhat greater distances to reposition the head on a different track, or (in some applications) may be moved to retract the head from the media. Such movements cause the first and second connectors 106, 108 (as seen in FIG. 3) to move relative to each other. During this movement, a biasing force directed against the movement by the rolling loop 102 is generally (i.e. more or less) constant.
Note that FIG. 1 illustrates a common configuration wherein the connectors 106, 108 at the ends of the ribbon cable 100 are oriented in parallel directions 110, 112, and also wherein the ribbon cable path between the connectors is oriented in a direction 114 that is perpendicular to the parallel directions 110, 112. (Note that line 114 is oriented from the center of one connector 106 to the center of another connector 108.) These geometric relationships tend to result in a biasing force that is exerted by the rolling loop that is generally quite low and that is substantially constant over an intended range of movement.
FIG. 2A illustrates that an arbitrarily selected conductor (i.e. a wire) passing through the rolling loop 102 of the ribbon cable 100 makes a turn that is partially circular (or partially elliptical). For example, a segment 202 of a single conductor is shown. That segment 202 makes a partial circular or partial elliptical turn within the rolling loop 102. If the length of the segment 202 were extended in a theoretical manner, the segment would form a circle or an ellipse. For example, circle 204 is formed by the theoretical extension of segment 202. (Circle 204 is offset for purposes of illustration, thereby avoiding superimposition over segment 202.)
Unfortunately, in some ribbon cable installations, the directions 110, 112 in which the connectors are oriented may not be perpendicular to the line 114 along which the ribbon cable is oriented. This can be caused, for example, by the necessity of moving one of the connectors—e.g. moving connector 106 in the direction of 110. Movement of a connector may be in response to form-factor and other geometrical constraints which simply do not allow the connectors 106, 108 to be positioned as desired and shown in FIG. 1.
Where the relationship of lines 104, 110–114, as seen above, is not present, the rolling loop 102 of the ribbon cable may not form a generally half-cylinder or parabolic shape—as seen in FIG. 3. Unfortunately, the resulting rolling loop which is not generally half-cylindrical or parabolic in shape may present a different biasing force resisting movement of the movable component to which one end of the ribbon cable is attached. In particular, the force required to move the movable component will typically be greater than, and less constant over a range of motion than, the force in the configuration of FIG. 1.
Therefore, in some applications the geometry of the components can result in problems associated with the bias force exerted by the ribbon cable 100 on a component to which the ribbon cable is attached. A solution to this problem would result in better control over a movable component attached to one end of the ribbon cable.